A long, unobstructed bomb bay meant that the Lancaster could take the largest bombs used by the RAF, including the 4,000 lb (1,800 kg), 8,000 lb (3,600 kg) and 12,000 lb (5,400 kg) blockbusters, loads often supplemented with smaller bombs or incendiaries. The "Lanc", as it was affectionately known,[3] became one of the more famous and most successful of the Second World War night bombers, "delivering 608,612 long tons of bombs in 156,000 sorties".[4] The versatility of the Lancaster was such that it was chosen to equip 617 Squadron and was modified to carry the Upkeep "Bouncing bomb" designed by Barnes Wallis for Operation Chastise, the attack on German Ruhr valley dams. Although the Lancaster was primarily a night bomber, it excelled in many other roles, including daylight precision bombing, for which some Lancasters were adapted to carry the 12,000 lb (5,400 kg) Tallboy and then the 22,000 lb (10,000 kg) Grand Slamearthquake bombs (also designed by Wallis).[5] This was the largest payload of any bomber in the war.

In the 1930s, the Royal Air Force (RAF) was primarily interested in twin-engine bombers.[7] These designs put limited demands on engine production and maintenance, both of which were already stretched with the introduction of so many new types into service. Power limitations were so serious that the British invested heavily in the development of huge engines in the 2,000 horsepower (1,500 kW) class in order to improve performance. During the late 1930s, none of these was ready for production. Both the United States and the Soviet Union were pursuing the development of bombers powered by arrangements of four smaller engines, the results of these projects proved to possess favourable characteristics such as excellent range and fair lifting capacity. Accordingly, in 1936, the RAF also decided to investigate the feasibility of the four-engined bomber.[7]

The origins of the Lancaster stem from a twin-engined bomber design that had been submitted in response to Specification P.13/36, which had been formulated and released by the British Air Ministry during the mid 1930s. This specification had sought a new generation of twin-engined medium bombers suitable for "worldwide use".[8] Further requirements of the specification included the use of a mid-mounted cantilevermonoplane wing, all-metal construction; the adoption of the in-development Rolls-Royce Vulture engine was also encouraged".[9] Various candidates were submitted for the specification by such manufacturers as Fairey, Boulton Paul, Handley Page and Shorts; all submissions were designed around two-engine configurations, using the Rolls-Royce Vulture, Napier Sabre, Fairey P.24 or Bristol Hercules engines. The majority of these engines were under development at this point; while four-engined bomber designs were considered for specification B.12/36 for a heavy bomber, wings which mounted two pairs of engines were still in the experimental stage and required testing at the Royal Aircraft Establishment (RAE), the resulting increase in overall weight of adopting a stronger wing also necessitated further strengthening of the overall aircraft structure.[10]

In response, British aviation company Avro decided to submit their own design, designated the Avro 679, to meet Specification P.13/36. In February 1937, following consideration of the designs by the Air Ministry, Avro's design submission was selected along with Handley Page's bid being chosen as "second string". Accordingly, during April 1937, a pair of prototypes of both designs were ordered.[11][9] The resulting aircraft, named the Manchester, entered RAF service in November 1940. Although considered to be a capable aircraft in most areas, the Manchester proved to be underpowered and troubled by the unreliability of the Vulture engine.[12] As a result, only 200 Manchesters were constructed and the type was quickly withdrawn from service in 1942.[13]

As early as mid-1940, Avro's chief design engineer, Roy Chadwick, had been working on an improved Manchester design.[12] This redesign was powered by four of the more reliable but less powerful Rolls-Royce Merlin engines, specifically adopted the form of the Merlin "Power Plant" installations which had been developed by Rolls-Royce for the earlier Beaufighter II, installed on a larger wing.[14] Initially, the improved aircraft was designated as the Type 683 Manchester III, it was subsequently renamed as the Lancaster. The prototype aircraft, serial numberBT308, was assembled by the Avro experimental flight department at Ringway Airport, Manchester; the prototype was constructed from a production Manchester airframe, which was combined with a new wing centre section designed to accommodate the additional engines.[12] On 9 January 1941, test pilot H. A. "Sam" Brown performed the prototype's maiden flight at RAF Ringway, Cheshire.

Lancaster bombers on Avro's Woodford assembly line at Cheshire, 1943

Flight testing of the new aircraft quickly proved it to be a substantial improvement on its predecessor, aviation author Jim Winchester referred to the Lancaster as being "one of the few warplanes in history to be 'right' from the start."[15] The first prototype was initially outfitted with a three-finned tail layout, a result of the design having been adapted from the Manchester I; this was quickly revised on the second prototype, DG595, and subsequent production Lancasters to the familiar larger elliptical twin-finned tail unit that had also been adopted for the later-built Manchesters, discarding the stubby central third tail fin.[12] The adoption of the enlarged twin fins not only increased stability but also provided for a greater field of fire from the dorsal gun turret position. The second prototype was also outfitted with more powerful Merlin XX engine.[12]

Some of the later orders for Manchesters were converted in favour of the Lancaster; both bombers shared various similarities and featured identical design features, such as the same distinctive greenhouse cockpit, turret nose and twin tail.[12] The designs were so similar that an entire batch of partially constructed Manchesters could be completed as Lancaster B I aircraft instead. Based upon its performance, a decision was taken early on to reequip twin-engine bomber squadrons with the Lancaster as quickly as possible.[12] In October 1941, the first production Lancaster, L7527, powered by Merlin XX engines, conducted its first flight.[12]

Lancasters under construction at Avro's factory at Woodford, Cheshire, 1943

Avro received an initial contract for 1,070 Lancasters.[12] The majority of Lancasters that were manufactured during the war years were constructed by Avro at their factory at Chadderton near Oldham, Greater Manchester and were test-flown from Woodford Aerodrome in Cheshire. As it was quickly recognised that Avro's capacity was exceeded by the wartime demand for the type, it was decided to form the Lancaster Aircraft Group, which comprised a number of companies that undertook the type's manufacture, either performing primary assembly themselves or producing various subsections and components for the other participating manufacturers.[16]

In addition to Avro, further Lancasters were constructed by Metropolitan-Vickers (1,080, also tested at Woodford) and Armstrong Whitworth. They were also produced at the Austin Motor Company works in Longbridge, Birmingham, later in the Second World War and post-war by Vickers-Armstrongs at Chester as well as at the Vickers Armstrong factory, Castle Bromwich, Birmingham. Belfast-based aircraft firm Short Brothers had also received an order for 200 Lancaster B Is, but this was cancelled before any aircraft had been completed.[17] Only 300 of the Lancaster B II, which was outfitted with Bristol Hercules engines, were constructed; this had been produced as a stopgap modification as a result of a shortage of Merlin engines due to fighter production having higher priority for the engines at that time.[citation needed]

The Lancaster was also produced overseas. During early 1942, it was decided that the bomber should be produced in Canada, where it was manufactured by Victory Aircraft in Malton, Ontario.[18] Of later variants, only the Canadian-built Lancaster B X was produced in significant numbers. A total of 430 of this type were built, earlier examples differing little from their British-built predecessors, except for using Packard-built Merlin engines and American-style instruments and electrics.[citation needed] In August 1942, a British-built Lancaster B I, R5727, was dispatched to Canada as a pattern aircraft, becoming the first of the type to conduct a transatlantic crossing.[18] The first Lancaster produced in Canada was named the "Ruhr Express".[Note 1][citation needed] The first batch of Canadian Lancasters delivered to England suffered from faulty ailerons; this error was subsequently traced to the use of unskilled labourers.[19]

The Lancaster B I was never fully superseded in production by a successor model, remaining in production until February 1946.[17] According to aviation authors Brian Goulding and M. Garbett, the Lancaster B I altered little during its production life, partially as a result of the sound basic structure and design; of the visible changes, the fuselage side-windows were deleted, the Perspex chin of the bomb-aimer was enlarged, and a larger astrodome was provided.[20] Various additional bumps and blisters were also added, which would typically house radar equipment and radio navigational aids. Some Lancaster B I bombers were outfitted with bulged bomb bay doors in order to accommodate increased armament payloads.[20]

Early production Lancaster B Is were outfitted with a ventral gun turret position.[18] In response to feedback on the lack of application for the ventral turret, the ventral turret was often eliminated during the course of each aircraft's career. While some groups chose to discard the position entirely, various trials and experiments were performed at RAF Duxford, Cambridgeshire and by individual squadrons.[18] A total of 50 Austin-built Lancaster B Is were constructed to a non-standard configuration, having a Frazer Nash turret installed directly above the bomb bay; this modification was largely unpopular due to its obstruction of the internal walkway, hindering crew movements. Various other turret configurations were adopted by individual squadrons, which included the removal of various combinations of turrets.[21]

The Lancaster B III was powered by Packard Merlin engines, which had been built overseas in the United States, but was otherwise identical to contemporary B Is.[17] In total, 3,030 B IIIs were constructed, almost all of them at Avro's Newton Heath factory. The Lancaster B I and B III were manufactured concurrently and minor modifications were made to both marks as further batches were ordered. The B I and B III designated was effective interchangeable simply by exchanging the engines used, which was occasionally done in practice.[17] Examples of modifications made include the relocation of the pitot head from the nose to the side of the cockpit and the change from de Havilland "needle blade" propellers to Hamilton Standard or Nash Kelvinator made "paddle blade" propellers.[22]

The Avro Lancaster was a British four-engined strategic bomber that was used as the RAF's principal heavy bomber during the latter half of the Second World War. The typical aircraft was powered by an arrangement of four wing-mounted Rolls-Royce Merlin piston engines, each of which drove a set of 13 ft diameter de Havilland Hydromatic three-bladed propellers. While not optimal, the Lancaster was capable of flying the return journey home on only two operational engines, along with very limited distances on a single running engine.[17] Goulding and Garbett have claimed that experienced Lancaster pilots were often able to out-manoeuver Luftwaffe fighters.[23] It possessed largely favourable flying characteristics, having been described by aviation authors Brian Goulding and M. Garbett as being: "a near-perfect flying machine, fast for its size and very smooth...such a delightfully easy aeroplane to fly...there are instances of Lancasters having been looped and barrel-rolled, both intentionally and otherwise".[23]

The Lancaster benefited from a structure that possessed considerable strength and durability, which had been intentionally designed to maximise structural strength-per-weight; this resulted in the Lancaster being capable of withstanding some levels of damage resulting from attacks by hostile interceptor aircraft and ground-based anti-aircraft batteries.[17] However, during the first year of the type's career, some instances of structural failures were encountered on Lancaster B Is and a number of aircraft were lost in accidents as a result of the design limitations having been greatly exceeded.[23] Compared with other contemporary aircraft, the Lancaster was not an easy aircraft to escape from; in a Halifax, 25 per cent of downed aircrew bailed out successfully, and in American bombers (albeit in daylight raids) it was as high as a 50 per cent success rate while only 15 per cent of the Lancaster crew were able to bail out.[24]

The Lancaster uses a mid-wing cantilevermonoplane configuration. The wing is constructed from five separate main sections while the fuselage is likewise composed of five sections. Aside from a few elements, such as the fabric-covered ailerons, the Lancaster's oval-shaped fuselage had an all-metal covering.[18] All of the wing and fuselage sections were manufactured separately, during which they were outfitted with all of the required equipment in advance of final assembly being performed, as a measure intended to accelerate the rate of production. The Lancaster was equipped with a retractable main undercarriage and fixed tailwheel; the hydraulically-actuated main landing gear raised rearwards into recesses within the inner engine nacelles.[25] The distinctive tail unit of the aircraft was outfitted with a large twin elliptical fins and rudder arrangement.[23]

The standard crew for a Lancaster consisted of seven men, stationed in various positions in the fuselage. Starting at the nose, the bomb aimer had two positions to man. His primary location was lying prone on the floor of the nose of the aircraft, with access to the bombsight controls facing forward, with the bombsight computer on his left and bomb release selectors on the right. He also used his view out of the large transparent perspex nose cupola to assist the navigator with map reading.[citation needed] To man the Frazer Nash FN5 nose turret, he stood up placing himself in position behind the triggers of the twin .303 in (7.7 mm) guns. Ammunition for the turret was 1,000 rounds per gun (rpg). The bomb aimer's position contained the nose emergency hatch in the floor; at 22 by 26.5 inches (560 by 670 mm) (two inches narrower than the Halifax escape hatch) it was difficult to exit through while wearing a parachute. Operational research experts, including British scientist Freeman Dyson, amongst others, attempted unsuccessfully to have the escape hatch enlarged.[citation needed]

On the roof of the bomb bay the pilot and flight engineer sat side by side under the expansive canopy, with the pilot sitting on the left on a raised portion of the floor (almost all British bombers, and most German bombers, had only a single pilot seat as opposed to American practice of carrying two pilots, or at least having controls for two pilots installed). The flight engineer sat on a collapsible seat (known as a "second dicky seat") to the pilot's right, with the fuel selectors and gauges on a panel behind him and to his right. The pilot and other crew members could use the panel above the cockpit as an auxiliary emergency exit while the mid-upper gunner was expected to use the rear entrance door to leave the aircraft. The tail gunner escaped by rotating his turret to the rear, opening the door in the back of the turret, passing into the fuselage, and clipping on a parachute that was hung on the side wall. He could then exit through the rear entrance door.[26]

Behind the pilot and flight engineer, and behind a curtain fitted to allow him to use light to work, sat the navigator. His position faced to port with a chart table in front of him. An instrument panel showing the airspeed, altitude, and other information required for navigation was mounted on the side of the fuselage above the chart table. The wireless operator's radios were mounted on the left-hand end of the chart table, facing the rear of the aircraft. Behind these and facing forwards the wireless operator sat on a seat at the front of the main spar. On his left was a window, and above him was the astrodome, used for visual signalling and by the navigator for celestial navigation.[citation needed]

Behind the wireless operator were the two spars for the wing, which created a major obstacle for crew members moving down the fuselage even on the ground. On reaching the end of the bomb bay the floor dropped down to the bottom of the fuselage, and the mid-upper gunner's turret was reached. His position allowed a 360° view over the top of the aircraft, with two Browning .303 Mark IIs to protect the aircraft from above and to the side. The mid-upper gunner sat on a rectangle of canvas that was slung beneath the turret and would stay in position throughout the flight. Ammunition for the turret was 1,000 rounds per gun.[citation needed]

To the rear of the turret was the side crew door, on the starboard side of the fuselage. This was the main entrance to the aircraft, and also could be used as an emergency exit. The Elsan chemical toilet, a type of aircraft lavatory, was located near the spars for the tailplane. At the extreme tail-end of the fuselage, the rear gunner sat in his exposed position in the tail turret, which was entered through a small hatch in the rear of the fuselage. Depending on the size of the rear gunner, the area was so cramped that the gunner would often hang his parachute on a hook inside the fuselage, near the turret doors. Neither the mid-upper nor the rear gunner's position was heated, and the gunners had to wear electrically heated suits to prevent hypothermia and frostbite.[citation needed]

Late on in the war, as a result of statistical analysis, Freeman Dyson put forward a case for the removal of the majority of the Lancaster's defensive armament. He argued that this would reduce the overall loss rate as it would have the benefit of increasing the Lancaster's cruise speed by up to 50 mph (80 km/h) (assuming the bomb load was not increased at the same time), and thus make the bomber harder to shoot down.[30] He also considered that the modification would be justified regardless of the envisioned decreased loss rate as, by requiring fewer crew to serve as defensive air gunners, that would be a lower number of human losses incurred with each aircraft lost.[31]

The ventral (underside) FN-64 turret quickly proved to be dead weight, being both difficult to sight because it relied on a periscope which limited the gunner's view to a 20 degree arc,[27] and too slow to keep a target within its sights.[Note 2] Aside from early B Is and the prototype B IIs, the FN-64 was almost never used. When the Luftwaffe began using Schräge Musik to make attacks from below in the winter of 1943/1944, modifications were made, including downward observation blisters mounted behind the bomb aimer's blister[32] and official[33] and unofficial mounts for .50 in (12.7 mm) machine guns or even 20 mm cannon, firing through the ventral holes of the removed FN-64. The fitting of these guns was hampered as the same ventral position was used for mounting the H2S blister, which limited installations to those aircraft fitted with bulged bomb bays which interfered with the H2S.[27]

The mid-upper (dorsal or top) turret was an FN-50[27][28] on early examples and the very similar FN-150 with improved sights and controls[27] on later examples. On all but the earliest examples this turret was surrounded by a coaming which provided a track for a cam operated interruptor device which prevented the gunner from shooting the tail of his own aircraft.[27] The Mk. VII and late Mk. X Lancasters used the heavier, electrically-controlled Martin 250 CE 23A turret equipped with two .50 inch machine guns[27] which was mounted further forward to preserve the aircraft's longitudinal balance, and because it had an internal mechanism to prevent firing on the aircraft itself, it did not require a coaming.[Note 3][27] Other experimental turrets were tried out, including the FN-79 and the Boulton-Paul Type H barbette system.[27]

The tail turret was the most important defensive position and carried the heaviest armament. Despite this, the turrets used, starting with the FN-20, were never entirely satisfactory and numerous designs were tried. The FN-20 was replaced by the very similar FN-120 which used an improved gyroscopic gun sight (GGS).[27] Many rear gunners insisted on having the centre section of perspex removed from the turret to improve visibility. The transparencies were difficult to see through at night, particularly when trying to keep watch for enemy night fighters that appeared without notice astern and below the aircraft when getting into position to open fire. This removal of perspex from the turret was called the "Gransden Lodge" modification. Ammunition for the tail turret was 2,500 rounds-per-gun. Due to the weight, the ammunition was stored in tanks situated near the mid-upper turret's position and fed rearward in runways down the back of the fuselage to the turret.[34]

Gunners using both the FN-20 and 120 removed perspex and armour from the turret to improve visibility, but trials by the RAF showed that a Mosquito night fighter was still able to get within a very short distance of the tail gunner without being spotted, confirming what the Luftwaffe had already realised. The Rose turret attempted to improve on the FN turrets by being completely open to the rear (improving visibility and allowing easier emergency egress) and by being fitted with two .50 inch machine guns and was installed in a small number of Lancasters but never became common.[27]

Ultimately radar, rather than improved visibility, made the turret more effective. The FN-121 was the Automatic Gun Laying Turret (AGLT), an FN-120 fitted with Village Inn gun-laying radar.[27] Aircraft fitted with Village Inn were used as bait, flying behind the main formations to confront the night fighters that followed the formations and shot down stragglers. This significantly reduced operational losses; and gun-laying radar was added to the last versions of the turret. Before the end of the war Lancasters built in the UK standardised on the FN-82 fitted with two .50 inch machine guns and fitted with gun-laying radar as production allowed, which was also used on early models of the Avro Lincoln. The disadvantage of all radar and radio transmitting systems is that attacking forces can locate aircraft by picking up transmissions.[citation needed]

In 1943, 617 Squadron was created to carry out Operation Chastise, the raid against the Ruhr dams. This unit was equipped with B.III (Specials), officially designated the "Type 464 (Provisioning)", modified to carry the 9,250 lb (4,200 kg) "Upkeep" bouncing bomb.[37][Note 4] The bomb bay doors were removed and the ends of the bomb bay were covered with fairings. "Upkeep" was suspended on laterally pivoted, vee-shaped struts which sprang apart beamwise when the bomb-release button was pressed. A drive belt and pulley to rotate the bomb at 500 rpm was mounted on the starboard strut and driven by a hydraulic motor housed in the forward fairing. The mid-upper turret was removed and a more bulbous bomb aimer's blister was fitted; this, as "Mod. 780", later becoming standard on all Lancasters, while the bombsight was replaced by a simple aiming device.[38] Two Aldis lights were fitted in the rear bomb bay fairing; the optimum height for dropping "Upkeep" was 60 ft and, when shone on the relatively smooth waters of the dam's reservoirs, the light beams converged into a single spot when the Lancaster was flying at the correct height.[39]

Towards the end of the war, attacking special and hardened targets, other variants of B I Specials were modified to carry the 21 ft (6.4 m) long 12,000 lb (5,400 kg) "Tallboy" or 25.5 ft (7.8 m) long 22,000 lb (10,000 kg) "Grand Slam" "earthquake" bombs. Aircraft intended to carry the "Grand Slam" required extensive modifications. These included the removal of the dorsal turret and of two guns from the rear turret, removal of the cockpit armour plating (the pilot's seatback), and installation of Rolls-Royce Merlin Mk 24 engines for better take-off performance. The bomb bay doors were removed and the rear end of the bomb bay cut away to clear the tail of the bomb. Later the nose turret was also removed to further improve performance. A strengthened undercarriage and stronger mainwheels, later used by the Avro Lincoln, were fitted.[5][Note 5]

Specific bomb loads were standardised and given code names by Bomber Command:[40]

Lancaster B I dropping 4 lb incendiaries followed by 30 lb incendiaries and finishing up with a 4,000 lb "cookie"

This was an early preset vector bombsight that involved squinting through wires that had to be manually set based on aircraft speed, altitude and bombload. This sight lacked tactical flexibility as it had to be manually adjusted if any of the parameters changed and was soon changed in favour of more advanced designs.

A vector bombsight where the bomb aimer input details of the bombload, target altitude and wind direction and the analogue computer then continuously calculated the trajectory of the bombs and projected an inverted sword shape onto a sighting glass on the sighting head. Assuming the sight was set correctly, when the target was in the cross hairs of the sword shape, the bomb aimer would be able to accurately release the bombs.

T1 bombsight

A Mark XIV bombsight modified for mass production and produced in the USA. Some of the pneumatic gyro drives on the Mk XIV sight were replaced with electronic gyros and other minor modifications were made.

The Lancaster had a very advanced communications system for its time. Most British-built Lancasters were fitted with the R1155 receiver and T1154 transmitter, whereas the Canadian-built aircraft and those built for service in the Far East had American radios. These provided radio direction-finding, as well as voice and Morse capabilities.

3 GHz frequency, ground-looking navigation radar system – eventually, it could be homed in on by the German night fighters' FuG 350 Naxos receiver and had to be used with discretion — a problem which the higher resolution, 10 GHz frequency American H2X radar never had to deal with. This is the large blister under the rear fuselage on later Lancasters.

A rearward-looking radar to warn of night fighter approaches. However, it could not distinguish between attacking enemy fighters and nearby friendly bombers and served as a homing beacon for suitably equipped German night fighters. Once this was realised after mid-July of 1944,[42] it was removed altogether.

A receiver for a navigation system of synchronised pulses transmitted from the UK – aircraft calculated their position from the time delay between pulses. The range of GEE was 3–400 mi (483–644 km). GEE used a whip aerial mounted on the top of the fuselage ahead of the mid-upper turret.

Boozer (radar detector)

A system of lights mounted on the aircraft's instrument panel that lit up when the aircraft was being tracked by the low-UHF band Würzburg-Riese ground radar and early model Lichtenstein B/C and C-1 airborne radar. In practice it was found to be more disconcerting than useful, as the lights were often triggered by false alerts in the radar-signal-infested skies over Germany.

A very accurate navigation system consisting of a receiver/transponder for two radar stations transmitting from widely separated locations in Southern England which, when used together, determined the aircraft's position. The system could only handle one aircraft at a time, and was fitted to a Pathfinder aircraft, usually a fast and manoeuvrable Mosquito which marked the target for the main force rather than a Lancaster.

A radar-aimed and ranged gun turret fitted to some Lancaster rear turrets in 1944. Identifiable by a radome mounted below the turret.

Airborne Cigar (ABC)

This was fitted only to the Lancasters of 101 Squadron. It had three 7-foot (2.1 m) aerials, two on the top of the fuselage and one under the bomb aimer's position. These aircraft carried a German-speaking crew member and were used to jam ground-to-air communications to German night fighters. The extra equipment and extra crewman added around 600 pounds (272 kg) to the bomber's weight so the bomb load was reduced by 1,000 pounds (454 kg).[43] Due to the nature of the equipment, the enemy was able to track the aircraft and 101 Squadron suffered the highest casualty rate of any squadron. Fitted from about mid-1943, they remained until the end of the war.

While the Lancaster had been designed to conduct night-time operations, daylight raids were occasionally performed by the type as well.[45] The existence of the Lancaster was revealed after a daytime raid upon an engine factory located in Augsburg, Swabia, Bavaria conducted by Nos. 44 and 97 Sqns on 17 April 1942. Due to the high loss rates typically involved in such operations, daytime bombing missions were performed sparingly until the Allies had achieved a level of aerial supremacy over the Axis powers.[45]

On 17 October 1942, another audacious daytime raid was performed by 90 Lancasters of No. 5 Group, bombing the Schneider Works at Le Creusot, France; only one aircraft was lost during the course of the mission.[45] During 1942, the Lancaster remained in relatively short supply, which meant that training and crew conversion courses typically had to be performed by the squadrons themselves; there were no aircraft furnished with dual controls at this time, thus pilots would have to perform their first flight without the instructor being capable of directly acting on the controls themselves.[45]

Throughout July 1943, large numbers of Lancasters participated in the devastating round-the-clock raids on the city of Hamburg during Air Chief Marshal Harris's "Operation Gomorrah". A particularly famous mission performed by the Lancaster was the mission flown 16- 17 May 1943, codenamed Operation Chastise, to destroy the dams of the Ruhr Valley. The operation was carried out by 617 Squadron in modified Mk IIIs carrying special drum-shaped bouncing bombs, which had been designed by British engineer Barnes Wallis. The story of the operation was later made into a film, The Dam Busters.

During the latter half of 1944, a series of high-profile bombing missions were performed by the Lancaster against the German battleship Tirpitz.[46] Executed by Nos. 617 and 9 Sqns, a combination of Lancaster B I and B III bombers were armed with 12,000 lb 'Tallboy' bombs and were adapted with enlarged bomb bay doors in order to accommodate their special payloads and additional fuel tanks to provide the necessary endurance. A total of three attacks, individually codenamed Operation Paravane, Operation Obviate and Operation Catechism, were conducted against Tirpitz, which was anchored in a fjord in Occupied Norway.[46] The first of these attacks disabled the vessel while the third mission was responsible for sinking the ship. As a result of actions such as Operation Chastise and the sinking of Tirpitz, No. 617 Sq was perhaps the most famous of all Lancaster squadrons.[45]

During early 1945, a total of 33 Lancaster B Is were modified so that they could deploy the 22,000 lb Grand Slam bomb; the Grand Slam, considered to be the ultimate conventional bomb to be used during the conflict, was so heavy that the bomb and the Lancaster itself weighed roughly the same.[47] On 13 March 1945, the first operational use of the Grand Slam was performed by a Lancaster of No. 617 Sqn against the Schildesche viaduct at Bielefeld, North Rhine-Westphalia. Amongst the final wartime operations performed by the Lancaster was the destruction of Eagle's Nest, the extensive holiday home complex used by German leader Adolf Hitler.[47]

RAF Lancasters dropped food into the Holland region of the occupied Netherlands, with the acquiescence of the occupying German forces, to feed people who were in danger of starvation.[47] The mission was named 'Operation Manna' after the food manna which is said to have miraculously appeared for the Israelites in the Book of Exodus. The aircraft involved were from 1, 3, and 8 Groups, and consisted of 145 Mosquitos and 3,156 Lancasters, flying between them a total of 3,298 sorties. The first of the two RAF Lancasters chosen for the test flight was nicknamed "Bad Penny" from the old expression: "a bad penny always turns up." This bomber, with a crew of seven men (five Canadians including pilot Robert Upcott of Windsor, Ontario), took off in bad weather on the morning of 29 April 1945 without a ceasefire agreement from the German forces, and successfully dropped its cargo.[citation needed]

The Lancaster conducted a total of 156,000 sorties and dropped 608,612 long tons (618,378 tonnes) of bombs between 1942 and 1945. Only 35 Lancasters completed more than 100 successful operations each, and 3,249 were lost in action. The most successful survivor completed 139 operations, and was ultimately retired from service and scrapped in 1947. From 1942 onwards, the Lancaster became the mainstay of the British heavy bomber fleet; by the end of the war in Europe, there were roughly 50 squadrons equipped with the Lancaster, the majority of these being the Lancaster B I model.[45] From its entry into service, the original model of the Lancaster was operated in almost every major bombing raid of the European conflict.[48]

Adolf Galland (commander of the Luftwaffe fighters) considered the Lancaster to be "the best night bomber of the war",[49] as did his adversary, Arthur "Bomber" Harris, who referred to it as the RAF Bomber Command's "shining sword".[50] Goulding and Garbett wrote that: "The achievements of the Lancaster and the men who flew it have been widely acclaimed, and the aircraft has been described as the greatest single factor in winning WWII, an exaggeration but a pardonable one".[23]

Lancasters from Bomber Command were to have formed the main strength of Tiger Force, the Commonwealth bomber contingent scheduled to take part in Operation Downfall, the codename for the planned invasion of Japan in late 1945.[48] Aircraft allocated to the Tiger Force were painted in white with black undersides and outfitted with additional radio units and navigational aids to facilitate their use in the Pacific theatre. The addition of large saddle-type external fuel tanks was considered and trialled in Australia and India, but this was discontinued due to their perceived vulnerability to attack.[51] Together with the new Avro Lincoln and Liberators, the bombers would have operated from bases on Okinawa; the envisioned invasion did not happen when such action was made unnecessary by the surrender of Japan.[48]

As a byproduct of its sound design and operational success, various developments and derivatives of the Lancaster were produced for both military and civilian purposes. One of these was the Avro Lincoln bomber, initially known as the Lancaster IV and Lancaster V. These two marks became the Lincoln B1 and B2 respectively. A civilian airliner was based on the Lancaster, known as the Lancastrian. Other developments were the York, a square-bodied transport and, via the Lincoln, the Shackleton which continued in RAF service as an airborne early warning (AEW) system, being in use until its retirement in 1992.

In the post-war climate, the Lancaster continued to see use for several more years, during which a number of high-profile operations were conducted.[52] Immediately following the end of hostilities, the Lancaster was used as a crude transport aircraft, being used to ferry thousands of prisoners of war (POWs) back to the British Isles from across the continent.[53] Aerial tours of the devastated German cities were also performed using the type. Repatriation flights returning POWs and ordinary troops alike continued until November 1945.[48] During the summer of 1946, Lancasters of No. 35 Squadron performed a tour of the United States. These aircraft were autographed by various American movie stars during the tour, and continued to bear these up to their retirements.[52] A pair of Lancasters, PD328 and PB873, performed several ground-breaking long distance flights, including round-the-world and trans-polar trips.[52]

In RAF service, the Lancaster remained at the forefront of Bomber Command; the Lancaster B I was gradually replaced by the improved Lancaster B I (F/E) models.[48] During 1947–1948, No. 82 Squadron received new dedicated photo-reconnaissance models of the Lancaster B.1; these aircraft were painted silver and lacked any defensive turrets. Photo-reconnaissance Lancasters with used to aerially survey Central and East Africa and at least one was later operated by the Ministry of Aviation.[52]Coastal Command received a small quantity of Lancasters, which were normally based at RAF Kinloss, Moray Firth.[52]

The Lancaster continued to be operated in significant numbers until the introduction of the new Avro Lincoln, being itself a derivative of the Lancaster; the Lincoln was not available in quantity for several years following the end of the conflict.[54] In December 1953, the final Lancaster in service with Bomber Command was retired.[48] In late 1954, the last Lancaster in active service with the RAF, an aircraft which had been used for aerial reconnaissance missions, is believed to have been retired.[55]

A total of 59 Lancaster B.Is and B.VIIs were overhauled by Avro at Woodford and Langar and delivered to the Aeronavale (France) during 1952/53.[56] These were flown until the mid-1960s by four squadrons stationed in France and New Caledonia in the maritime reconnaissance and search-and-rescue roles.[57]

Between 1948 and 1949, a total of 15 former RAF Lancasters were overhauled at Langar for use by the Argentine Air Force.[56] During its Argentine service, Lancasters were used offensively in suppressing and supporting military coups.[58]

Beginning in 1946, Lancaster Mk Xs were modified for service with the Royal Canadian Air Force (RCAF). Fourteen aircraft were modified to perform aerial and photo-reconnaissance missions; these would go on to perform much of the mapping of northern Canada until as late as 1962. Throughout the 1950s, the RCAF operated seventy modified Lancasters, designated Lancaster 10MR/MPs, as Maritime Reconnaissance and Patrol aircraft in an anti-submarine role. Modifications involved the installation of radar and sonobuoy operators' positions, removal of the rear and mid-upper gun turrets, installation of a 400-gallon fuel tank in the bomb bay to increase the patrol range, upgraded electronics, radar, and instrumentation, and a cooking stove in the centre section.[59] They served throughout the 1950s, when they were replaced by the Lockheed Neptune and Canadair Argus.[60]

Civil conversions of the type continued during the initial postwar years. In 1946, four Lancasters were converted by Avro at Bracebridge Heath, Lincolnshire as freighters for use by British South American Airways, but proved to be uneconomical, and were withdrawn after a year in service. In addition, four Lancaster IIIs were converted by Flight Refuelling Limited as two pairs of tanker and receiver aircraft for development of in-flight refuelling. In 1947, one aircraft was flown non-stop 3,459 mi (5,567 km) from London to Bermuda. Later on, these two tanker aircraft were joined by another converted Lancaster; these saw use during the Berlin Airlift, achieving 757 tanker sorties.[citation needed]

From 1943 to 1947, the Canadian Government Trans-Atlantic Air Service (CGTAS) provided a trans-Atlantic military passenger and postal delivery service using a modified long-distance transport version of the Lancaster Mark X. Nine of these aircraft were produced, referred to as Lancaster XPPs (for Lancaster Mk.X Passenger Planes), and each was equipped with rudimentary passenger facilities. The inaugural flight from Dorval (Montreal) to Prestwick, Scotland on 22 July 1943, was completed non-stop in a record 12:26 hours; the average crossing time was about 13:25 hours. By the end of the war, these aircraft had completed hundreds of trips across the Atlantic. CGTAS ushered in the era of commercial air travel across the North Atlantic, and in 1947 the service became part of Trans-Canada Air Lines, which carried paying civilian passengers in the Lancaster XPPs until they were replaced by Douglas DC-4s in 1947.[60][61][62]

The original Lancasters were produced with Rolls-Royce Merlin XX engines and SUcarburettors. Minor details were changed throughout the production series – for example the pitot head design was changed from being on a long mast at the front of the nose to a short fairing mounted on the side of the fuselage under the cockpit. Later production Lancasters had Merlin 22 and 24 engines. No designation change was made to denote these alterations.[63]

B.I Special

B1 Special releasing Grand Slam

32 Aircraft were adapted to take first the super-heavy "Tallboy" and then "Grand Slam" bombs. Up-rated engines with paddle-bladed propellers gave more power, and the removal of gun turrets reduced weight and gave smoother lines. For the Tallboy, the bomb bay doors were bulged; for the Grand Slam, they were removed completely and the area faired over. For some Tallboy raids, the mid-upper turret was removed. This modification was retained for the Grand Slam aircraft, and in addition the nose turret was later removed. Two airframes (HK541 and SW244) were modified to carry a dorsal "saddle tank" with 1,200 gal (5,455 L) mounted aft of a modified canopy for increasing range. No. 1577 SD Flight tested the aircraft in India and Australia in 1945 for possible use in the Pacific,[28] but the tank adversely affected handling characteristics when full and an early type of in-flight refuelling designed in the late 1930s for commercial flying boats was later used instead.[64]

B 1 modified for photographic reconnaissance, operated by RAF No. 82 and No. 541 Squadrons, wartime. All armament and turrets were removed with a reconfigured nose and a camera carried in the bomb bay. The type was also operated by 683(PR) Squadron when it was re-formed in November 1950 to undertake photographic reconnaissance and mapping activities, initially based at RAF Fayid, Egypt, before moving to RAF Kabrit in February 1951, and subsequently Habbaniya in Iraq until the squadron was disbanded on 30 November 1953.[citation needed]

B.I (FE)

In anticipation of the needs of the Tiger Force operations against the Japanese in the Far East (FE), a tropicalised variant was based on late production aircraft. The B I (FE) had modified radio, radar, navaids, and a 400 gal (1,818 L) tank installed in the bomb bay. Most were painted with white upper-surfaces to reduce internal temperatures in the tropical sun, and black undersides with a low demarcation between the colours, completely omitting any red colours on the national insignia in all cases to avoid confusion with the hinomaru insignia of the Japanese.[citation needed]

Bristol Hercules (Hercules VI or XVI engines) powered variant, of which 300 were produced by Armstrong Whitworth. One difference between the two engine versions was that the VI had manual mixture control, requiring an extra lever on the throttle pedestal. Very early examples were fitted with an FN.64 ventral turret; however, these were quickly removed due to problems with aiming the turret through its periscope (which prevented the gunner from seeing a target he was not already aiming at), and inadequate traverse speed.[citation needed]

Due to the Luftwaffe Schräge Musik attacks, a variety of unofficial field modifications were made, including fitting of 20 mm cannon or a .50 inch machine gun in the open hole where the FN.64 had been installed, before an official modification (Mod 925) fitted with a .303 inch machine gun was authorised for the same location, though not in all aircraft. These were rarely installed on other variants as the H2S radar that was not used on the B II was mounted there. Three types of bulged bomb bay were used on the B II, the prototype having a narrow bulge running from just aft of the cockpit to the end of the bomb bay, while early production examples had a full width bulge that ran the same length and on late production examples the bomb bay doors were prominently bulged throughout their length.[citation needed]

B.III

This variant, which was built concurrently with the B I and was indistinguishable externally from that variant, was fitted with Packard-built Merlin engines. The Packard Merlins used Bendix – Stromberg pressure-injection carburettors, requiring the addition of slow-running cut-off switches in the cockpit.[citation needed]

B.III (Special)

"Upkeep" bouncing bomb used for dam busting bomb mounted under Lancaster B III (Special). The chain was driven by a hydraulic motor and gave the bomb its backspin.

Known at the time of modification as the "Type 464 Provisioning"[65] Lancaster, 23 aircraft of this type were built to carry the "Upkeep" bouncing bomb for the dam busting raids. The bomb bay doors were removed and Vickers-built struts to carry the bomb were fitted in their place at Woodford Aerodrome near Stockport where the workers worked day and night. A hydraulic motor, driven by the pump previously used for the mid-upper turret was fitted to spin the bomb. Lamps were fitted in the bomb bay and nose for the simple height measurement system which enabled the accurate control of low-flying altitude at night. The mid-upper turret was removed to save weight and the gunner moved to the front turret to relieve the bomb aimer from having to man the front guns so that he could assist with map reading.[citation needed]

ASR.III/ASR.3

B.III modified for air-sea rescue, with three dipole ventral antennas fitted aft of the radome and carrying an airborne lifeboat in an adapted bomb bay. The armament was often removed and the mid-upper turret faired-over, especially in postwar use. Observation windows were added to both sides of the rear fuselage, a port window just forward of the tailplane and a starboard window into the rear access door. A number of ASR 3 conversions were fitted with Lincoln-style rudders.[66]

The B.IV featured an increased wingspan and lengthened fuselage and new Boulton Paul F turret (two X 0.5in Browning machine guns) with framed "bay window" nose glazing. The prototypes (PW925, PW929 and PW932) were powered by two-stage Merlin 85s inboard and later, Merlin 68s on the outboard mounts. Because of the major redesign, the aircraft was quickly renamed Lincoln B 1.[67]

Nine aircraft converted from B.IIIs. Fitted with Merlin 85/87 which had two-stage superchargers, giving much improved high altitude performance. The B VI could achieve a maximum speed of 313 mph (505 km/h) at 18,200 ft (5,550 m) at 65,000 lb (29,500 kg) takeoff weight and a service ceiling of 28,500 ft (8,690 m) at the same weight. Climb to 28,000 ft (8,500 m) at 65,000 lb (29,500 kg) takeoff weight was accomplished in 44.8 minutes with a maximum climb rate of 1,080 ft/min (5.5 m/s) at 1,000 ft (305 m).[68] A Lancaster B VI was dived to a maximum indicated speed of 350 mph (565 km/h), or Mach 0.72 at 25,000 ft (7,620 m) in June 1944.[69] The Merlin 85/87 series engines were fitted with annular cowlings similar to the Avro Lincoln and three bladed paddle-type propellers were fitted. These aircraft were only used by Pathfinder units; by No. 7 Squadron RAF, No. 83 Squadron RAF, No. 405 Squadron RCAF and by No. 635 Squadron RAF. Often used as a "Master Bomber" the B VI's were allocated to RAF Bomber Command apart from two that were retained by Rolls-Royce for installation and flight testing.[70] Their dorsal and nose turrets were removed and faired-over. The more powerful engines proved troublesome in service and were disliked by ground maintenance staff for their rough running and propensity to 'surge and hunt', making synchronisation impossible. This was caused by variations in the fuel/air mixture and over time would damage the engine.[71] The B VI was withdrawn from operational service in November 1944 and surviving aircraft were used by Rolls-Royce, the Royal Aircraft Establishment and the Bomb Ballistics Unit (BBU) for various testing and experimental duties.[citation needed]

B.VII

The B.VII was the final production version of the Lancaster. The Martin 250CE mid-upper turret was moved slightly further forward than on previous Marks and the Nash & Thomson FN-82 tail turret with twin 0.50 in (12.7 mm) Browning machine guns replaced the FN.20 turret with four Browning .303 Mark IIs. The Martin turret carried two 0.5 inch Browning Mark II machine guns which packed much more punch than the .303s of the older turret. However, these Martin turrets arrived too late for inclusion in the first 50 aircraft built by Austin and these were therefore referred to as Mark VII (Interim). Another 180 true Mark VIIs were built at Longbridge. Two sub-variants of the VII existed, the "Far East" (B VII FE) for use in tropical climates and the B VII "Western Union", which went to France.[citation needed]

B.X

Propaganda shot before bombing up an RCAF 428 Squadron B Mk X. This aircraft carries the early "needle-blade" propellers.

The B.X was a Canadian-built B.III with Canadian- and US-made instruments and electrics. On later batches the heavier Martin 250CE was substituted for the Nash & Thomson FN-50 mid-upper turret, mounted further forward to maintain centre of gravity balance. Canada was a long term operator of the Lancaster, using modified aircraft after the war for maritime patrol, search and rescue and photo-reconnaissance until 1964. The last flight by the RCAF was by F/L Lynn Garrison in KB-976, on 4 July 1964 at the Calgary International Air Show.[citation needed]

During the Second World War, Canada's Victory Aircraft (what later became Avro Canada) was responsible for the development of the Lancastrian, which was duly designated the XPP for Mark 10 Passenger Plane. Six were built for Trans Canada Airlines.

Postwar the RCAF modified the B X (as the Lancaster Mk 10) to fill a variety of roles, with specific designations for each role. These included:

10AR: Area Reconnaissance – three aircraft modified for surveillance operations over the Arctic. Fitted with lengthened nose (40 inches (100 cm) longer) and carrying cameras and ELINT equipment. Remained in service until 1964.[72]

Of the 17 surviving and largely intact Lancasters known to exist, two are airworthy; one, PA474, based in Coningsby, the UK, is operated by The Battle of Britain Memorial Flight, and the other, called Vera (coded VR-A, FM213), is in Canada, operated by the Canadian Warplane Heritage Museum in Mount Hope, a suburb of Hamilton, Ontario. Another Lancaster, Just Jane, NX611, a B MkVII, based in East Kirkby Lincolnshire Aviation Heritage Centre is able to taxi but is not currently airworthy, though there are plans to return her to flight in the future. The fourth Lancaster with working engines and able to taxi is Bazalgette FM159 based at the Bomber Command Museum of Canada in Nanton, Alberta. It has been carefully restored from a vandalised state and is now a main tourist attraction.

In 2014, the Canadian aircraft toured the UK in a series of joint displays with the BBMF aircraft.[81]

For the 2018 flying season, to commemorate the 75th anniversary of Operation Chastise, the Canadian Warplane Heritage Lancaster is painted in the markings of Guy Gibson's 617 Squadron aircraft (Code AJ-G, ED932) when he commanded the "Dambusters" raids.[83]

The Avro Lancaster featured prominently in the 1955 film The Dam Busters, and a number of B VII Lancasters in storage were modified to the original configuration of the B III (Special) for use on screen.[citation needed]

1.
Avro Lancaster PA474
–
PA474 is one of only two Lancasters in flying condition in the world, the other being owned and flown by the Canadian Warplane Heritage Museum. PA474 was built by Vickers-Armstrongs Ltd at its Broughton factory near Chester in 1945 and was to be part of the British Tiger Force for strategic bombing in the Far East, with the end of the war with Japan the aircraft was not needed and PA474 entered storage. With gun turrets removed it was assigned to Photographic Reconnaissance duties with 82 Squadron in East, on return from squadron service PA474 was loaned to Flight Refuelling Limited to be used as a pilotless drone. Flight Refuelling used an Avro Lincoln instead and PA474 was then transferred to the College of Aeronautics, Cranfield, the test wings were mounted vertically above the rear fuselage. In 1964 PA474 came under the control of the Air Historical Branch for possible display in the proposed RAF Museum, during this time the aircraft appeared in two films, Operation Crossbow and The Guns of Navarone. Following a request from 44 Squadron the Lancaster moved to RAF Waddington for restoration back to wartime standard including fitting back the front, PA474 was transferred to the Battle of Britain Memorial Flight in 1973. In 1975 a mid-upper turret was found in Argentina and fitted, during the winter of 1995 the Lancaster was fitted with a new main spar to extend the flying life. On 7 May 2015, the aircraft suffered a fire in its outer engine. A safe landing was made at RAF Coningsby and it flew again on 12 October 2015 after extensive work to fix the damaged caused by the fire to number four engine. It was later announced that with the maintenance, PA474 should still be airworthy until 2065. List of surviving Avro Lancasters Battle of Britain Memorial Flight, Lancaster PA474, RAF, Archived from the original on July 27,2013 CS1 maint, Unfit url Battle Of Britain Memorial Flight page

2.
Heavy bomber
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Heavy bombers are bomber aircraft with the greatest bomb load carrying capacity and longest range of their time. They have also typically been among the largest size aircraft in military or civil service. Delivery of the largest possible amount of air-to-ground weaponry over long distances to strike enemy targets is the heavy bombers mission, availability of such large, long range aircraft in mass-produced quantity also allowed methodologies of strategic bombing to be developed and employed during the 1940s. In August 1945, the U. S. B-29 heavy bombers delivered two atomic bombs against enemy targets, the arrival of nuclear weapons permanently changed the nature of warfare and military strategy. After the 1950s intercontinental ballistic missiles and ballistic missile submarines began to supersede heavy bombers in the nuclear role. Russian and U. S. heavy bombers have been used in regional conflicts since World War II delivering conventional weapons only. Heavy bombers are today only retained in service by the U. S, Russia and China for strategic bombing and tactical bombing roles. The first heavy bomber was designed as an airliner, igor Sikorsky, an engineer educated in St Petersburg, but born in Kiev of Polish-Russian ancestry designed the Sikorsky Ilya Muromets to fly between his birthplace and his new home. It did so briefly until August 1914, when the Russo-Balt wagon factory converted to a bomber version, by December 1914 a squadron of 10 was bombing German positions on the Eastern Front and by summer 1916 there were twenty. It was well-armed with nine guns, including a tail gun. It had a wingspan just a few feet shorter but a load of just 3% of a WW II Avro Lancaster. The Handley Page Type O/100 owed a lot to Sikorskys ideas, of similar size, it used just two Rolls-Royce Eagle engines and could carry up to 2,000 lb of bombs. But after one was lost, it switched to night attacks, one was used to support T. E. Lawrences Sinai and Palestine Campaign. The Imperial German Air Service operated the Gotha bomber, which developed a series of marques, the Gotha G. IV operated from occupied Belgium from the Spring of 1917. It mounted several raids on London beginning in May 1917, some reached no further than Folkestone or Sheerness on the Kent Coast. But on June 13, Gothas killed 162 civilians, including 18 children in a primary school, initially defence against air attack was poor, but by May 19,1918, when 38 Gothas attacked London, six were shot down and another crashed on landing. German aircraft companies also built a number of giant bombers, collectively known as the Riesenflugzeug, most were produced in very small numbers from 1917 onwards and several never entered service. The most numerous were the Zeppelin-Staaken R. VI of which 13 saw service, bombing Russia and London, four were shot down and they were larger than the standard Luftwaffe bombers of World War II

3.
Royal Air Force
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The Royal Air Force is the United Kingdoms aerial warfare force. Formed towards the end of the First World War on 1 April 1918, following victory over the Central Powers in 1918 the RAF emerged as, at the time, the largest air force in the world. The RAF describe its mission statement as, an agile, adaptable and capable Air Force that, person for person, is second to none, and that makes a decisive air power contribution in support of the UK Defence Mission. The mission statement is supported by the RAFs definition of air power, Air power is defined as the ability to project power from the air and space to influence the behaviour of people or the course of events. Today the Royal Air Force maintains a fleet of various types of aircraft. The majority of the RAFs rotary-wing aircraft form part of the tri-service Joint Helicopter Command in support of ground forces, most of the RAFs aircraft and personnel are based in the UK, with many others serving on operations or at long-established overseas bases. It was founded on 1 April 1918, with headquarters located in the former Hotel Cecil, during the First World War, by the amalgamation of the Royal Flying Corps, at that time it was the largest air force in the world. The RAFs naval aviation branch, the Fleet Air Arm, was founded in 1924, the RAF developed the doctrine of strategic bombing which led to the construction of long-range bombers and became its main bombing strategy in the Second World War. The RAF underwent rapid expansion prior to and during the Second World War, under the British Commonwealth Air Training Plan of December 1939, the air forces of British Commonwealth countries trained and formed Article XV squadrons for service with RAF formations. Many individual personnel from countries, and exiles from occupied Europe. By the end of the war the Royal Canadian Air Force had contributed more than 30 squadrons to serve in RAF formations, additionally, the Royal Australian Air Force represented around nine percent of all RAF personnel who served in the European and Mediterranean theatres. In the Battle of Britain in 1940, the RAF defended the skies over Britain against the numerically superior German Luftwaffe, the largest RAF effort during the war was the strategic bombing campaign against Germany by Bomber Command. Following victory in the Second World War, the RAF underwent significant re-organisation, during the early stages of the Cold War, one of the first major operations undertaken by the Royal Air Force was in 1948 and the Berlin Airlift, codenamed Operation Plainfire. Before Britain developed its own nuclear weapons the RAF was provided with American nuclear weapons under Project E and these were initially armed with nuclear gravity bombs, later being equipped with the Blue Steel missile. Following the development of the Royal Navys Polaris submarines, the nuclear deterrent passed to the navys submarines on 30 June 1969. With the introduction of Polaris, the RAFs strategic nuclear role was reduced to a tactical one and this tactical role was continued by the V bombers into the 1980s and until 1998 by Tornado GR1s. For much of the Cold War the primary role of the RAF was the defence of Western Europe against potential attack by the Soviet Union, with many squadrons based in West Germany. With the decline of the British Empire, global operations were scaled back, despite this, the RAF fought in many battles in the Cold War period

4.
Royal Canadian Air Force
–
The Royal Canadian Air Force is the air force of Canada. Its role is to provide the Canadian Forces with relevant, responsive and effective airpower, the RCAF is one of three environmental commands within the unified Canadian Armed Forces. Lieutenant-General Michael J. Hood, CMM CD, is the current Commander of the Royal Canadian Air Force, the RCAF is a partner with the United States Air Force in protecting continental airspace under the North American Aerospace Defense Command. The RCAF also provides all primary air resources to and is responsible for the National Search, the RCAF traces its history to the Canadian Air Force which was formed in 1920. The Canadian Air Force was incorporated in 1923 and granted royal sanction in 1924 by King George V, in 1968 the RCAF was amalgamated with the Royal Canadian Navy, and the Canadian Army, as part of the unification of the Canadian Forces. Air units were split between several different commands, Air Defence Command, Air Transport Command, Mobile Command, Maritime Command, in 1975 some commands were dissolved, and all air units were placed under a new environmental command called simply Air Command. Air Command reverted to its name of the Royal Canadian Air Force in August 2011. The Royal Canadian Air Force has served in the Second World War, the Korean War, as a NATO member, the force maintained a presence in Europe during the second half of the 20th century. The Canadian Air Force was established in 1920 as the successor to a short-lived two-squadron Canadian Air Force formed during the First World War in Europe. John Scott Williams, MC, AFC, was tasked in 1921 with organizing the CAF, the new Canadian Air Force was a branch of the Air Board and was chiefly a training militia that provided refresher training to veteran pilots. Many CAF members also worked with the Air Boards Civil Operations Branch on operations that included forestry, in 1923, the CAF became responsible for all flying operations in Canada, including civil aviation. In 1924, the Canadian Air Force, was granted the royal title, most of its work was civil in nature, however, in the late 1920s the RCAF evolved into more of a military organization. After budget cuts in the early 1930s, the air began to rebuild. By the end of the war, the RCAF had become the fourth largest allied air force, after the war, the RCAF reduced its strength. In 1950, the RCAF became involved with the transport of troops and supplies to the Korean War, however, members of the RCAF served in USAF units as exchange officers and several flew in combat. Both auxiliary and regular air defence squadrons were run by Air Defence Command, at the same time, the Pinetree Line, the Mid-Canada Line and the DEW Line radar stations, largely operated by the RCAF, were built across Canada because of the growing Soviet nuclear threat. In 1957, Canada and the United States created the joint North American Air Defense Command, coastal defence and peacekeeping also became priorities during the 1950s and 1960s. In 1968 the Royal Canadian Navy, Royal Canadian Air Force and this initiative was overseen by then Liberal Defence Minister, Paul Hellyer

5.
Royal Australian Air Force
–
The Royal Australian Air Force, formed March 1921, is the aerial warfare branch of the Australian Defence Force. It directly continues the traditions of the Australian Flying Corps, formed on 22 October 1912, the RAAF provides support across a spectrum of operations such as air superiority, precision strikes, intelligence, surveillance and reconnaissance, air mobility, and humanitarian support. The RAAF has taken part in many of the 20th centurys major conflicts, thousands of Australians also served with other Commonwealth air forces in Europe. By the time the war ended, a total of 216,900 men and women served in the RAAF, later the RAAF served in the Berlin Airlift, Korean War, Malayan Emergency, Indonesia–Malaysia Confrontation and Vietnam War. More recently, the RAAF has participated in operations in East Timor, the Iraq War, the War in Afghanistan, and the intervention against the Islamic State of Iraq. The RAAF has 259 aircraft, of which 110 are combat aircraft, the RAAF traces its history back to the Imperial Conference held in London in 1911, where it was decided aviation should be developed within the armed forces of the British Empire. By 1914 the corps was known as the Australian Flying Corps, soon after the outbreak of war in 1914, the Australian Flying Corps sent aircraft to assist in capturing German colonies in what is now north-east New Guinea. However, these colonies surrendered quickly, before the planes were even unpacked, the first operational flights did not occur until 27 May 1915, when the Mesopotamian Half Flight was called upon to assist the Indian Army in protecting British oil interests in what is now Iraq. The corps later saw action in Egypt, Palestine and on the Western Front throughout the remainder of the First World War, by the end of the war, four squadrons—Nos. 1,2,3 and 4—had seen operational service, while another four training squadrons—Nos,5,6,7 and 8—had also been established. A total of 460 officers and 2,234 other ranks served in the AFC, casualties included 175 dead,111 wounded,6 gassed and 40 captured. The Australian Flying Corps remained part of the Australian Army until 1919, although the Central Flying School continued to operate at Point Cook, military flying virtually ceased until 1920, when the Australian Air Corps was formed. The Australian Air Force was formed on 31 March 1921, king George V approved the prefix Royal in June 1921 and became effective on 31 August 1921. The RAAF then became the second Royal air arm to be formed in the British Commonwealth, when formed the RAAF had more aircraft than personnel, with 21 officers and 128 other ranks and 153 aircraft. A total of 17 RAAF bomber, fighter, reconnaissance and other squadrons served initially in Britain and with the Desert Air Force located in North Africa, thousands of Australians also served with other Commonwealth air forces in Europe during the Second World War. About nine percent of the personnel who served under British RAF commands in Europe and this statistic is further illustrated by the fact that No.460 Squadron RAAF, mostly flying Avro Lancasters, had an official establishment of about 200 aircrew and yet had 1,018 combat deaths. The squadron was therefore effectively wiped out five times over, total RAAF casualties in Europe were 5,488 killed or missing. The beginning of the Pacific War—and the rapid advance of Japanese forces—threatened the Australian mainland for the first time in its history, the RAAF was quite unprepared for the emergency, and initially had negligible forces available for service in the Pacific

6.
Avro Manchester
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The Avro 679 Manchester was a British twin-engine heavy bomber developed during the Second World War by the Avro aircraft company in the United Kingdom. Serving in the Royal Air Force and Royal Canadian Air Force, the aircraft was the forerunner of the successful four-engined Avro Lancaster, which would become one of the most capable strategic bombers of the war. The Manchester was originally designed to the Air Ministry Specification P. 13/36, provision for catapult assisted takeoff to permit the maximum load was also part of the specification, although the need for this provision was explicitly removed in July 1938. Cruising speed was to be a minimum of 275 mph at 15,000 feet, the Air Ministry had expectations for an aircraft of similar weight to the B. 1/35 specification, but being both smaller and faster. Avro had already started work on a design before the invitation to tender and they were in competition with Boulton Paul, Bristol, Fairey, Handley Page and Shorts. Vickers had the Warwick with Napier Sabre engines but did not tender it. In early 1937, the Avro design and the rival Handley Page HP.56 were accepted and this skipping of the usual process was necessary due to the initiation of a wider expansion of the RAF in expectation of war. From 1939, it was expected that the P. 13/36 would replace existing medium bombers, such as the Armstrong Whitworth Whitley, Handley Page Hampden and Vickers Wellington. When developed in 1935, the Vulture engine had promise — it was rated at 1,760 hp but it proved unreliable and had to be derated to 1. The Handley Page HP.56, always intended as the backup to the Avro, was redesigned to take four engines on the orders of the Air Ministry in 1937, when the Vulture was already showing problems. While the Manchester was designed with a tail, the first production aircraft, designated the Mk I, had a central fin added. They were succeeded by the Mk IA which reverted to the system but used enlarged, taller fin and rudders mounted on a new tailplane. This configuration was carried over to the Lancaster, except for the first prototype, Avro constructed 177 Manchesters while Metropolitan-Vickers completed 32 aircraft. Plans for Armstrong Whitworth and Fairey Aviation at Stockport/Ringway to build the Manchester were abandoned, faireys order for 150 Manchesters was replaced by multiple orders for the Handley Page Halifax. The Avro Manchester was designed with consideration for ease of manufacture. The fuselage of the aircraft comprised longitudinal stringers or longerons throughout, the wings were of a two-spar construction, the internal ribs being made of aluminium alloys, fuel was contained with several self-sealing fuel tanks within the wings. The tail shared a similar construction to the wing, featuring a twin fin-and-rudder configuration that provided good vision for the dorsal gunner, the cockpit housed the pilot and fighting controllers position underneath the canopy, and these two crew members were provided with all-round vision. The navigator was seated aft of the controller and the position included an astrodome for use of a sextant

7.
Avro York
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The Avro York was a British transport aircraft developed by Avro during the Second World War. The design was derived from the famed Avro Lancaster heavy bomber that was being produced at the time for the Royal Air Force, several sections of the York and Lancaster were identical. Due to priority being placed on the Lancaster instead, production of the York proceeded at a pace until 1944. The York saw service in military and civilian roles with various operators between 1943 and 1964. In civilian service, the British Overseas Airways Corporation was the most prolific user of the type, in military service, large numbers of Yorks were used during the high-profile air-supply missions during the Berlin Blockade 1948–49. During 1941, Avro elected to begin development of a new civil-orientated transport aircraft, roy Chadwick, Avros chief designer, had foreseen a need for a transport aircraft that was powered by four-engines and would be capable of flying for long ranges. The design, which was designated as the Type 685, had its origins in the companys then-newly developed four-engined bomber, the Avro Lancaster, the two aircraft also substantially differed in external appearance. In February 1942, Chadwick submitted his drawings to Avros experimental department, within five months, the company refined the design and had quickly assembled an initial prototype. On 5 July 1942, the York prototype, LV626, conducted its maiden flight from Ringway Airport, Flight trials of LV626 were quickly transferred to RAF Boscombe Down. 1/42, part of Operational Requirement OR.113 for a new transport aircraft. The prototypes were used to test various adaptions and potential roles for the aircraft, LV626, the first prototype, was rebuilt to the C. Production of the York proved difficult to speed up due to shortages of key materials, Avro was also obligated to place a priority on the manufacturing. Officials had also judged that there was no requirement for large numbers of Yorks at that time, by the end of 1943, only the four prototypes and three production aircraft had been manufactured, however production was scheduled to rise to three aircraft per month throughout 1944. Early production Yorks were principally used as a VIP transport aircraft, notably, the first RAF production order consisted of 200 aircraft, while a further 100 were ordered under a second order placed shortly after. Throughout 1944, the majority of Yorks produced were passenger transport aircraft, only eight aircraft of the second order for 100 aircraft were produced, in April 1948, the final York, PE108, was completed. A single pattern aircraft was completed by Victory Aircraft in Canada, however, Victory had tooled up for the manufacture of 30 aircraft and had built parts for five aircraft, ultimately, one would be completed around the time that the war came to an end. This aircraft would later be purchased by Swedish airline Skyways, the Avro York is a high-wing cantilever monoplane using an all-metal construction, bearing many similarities to the Lancaster from which it was derived. The wings use a structure, which internally housed seven fuel tanks contained 2,478 gallons between the spars. The outboard panels of the wings are tapered on both edges and are furnished with detachable tips, the wings feature all-metal hydraulically-actuated split trailing edge flaps and carry the four Rolls-Royce Merlin engines in four underslung nacelles attached to the front wing spar

8.
Avro Lincoln
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The Avro Type 694, better known as the Avro Lincoln, was a British four-engined heavy bomber, which first flew on 9 June 1944. Developed from the Avro Lancaster, the first Lincoln variants were known initially as the Lancaster IV and V but were renamed Lincoln I and it was the last piston-engined bomber used by the Royal Air Force. The Lincoln became operational in August 1945, the Lincoln was used in action during the 1950s, by the RAF in the Mau Mau Uprising in Kenya and with the RAF and RAAF during the Malayan Emergency. The type also saw significant service with the Royal Australian Air Force, in Argentine service it was also replaced by the Canberra. The Avro Lincoln was Roy Chadwicks development of the Lancaster, built to the Air Ministry Specification B.5 tons of various armaments and equipment fittings. As a result of changes, the Lincoln had a higher operational ceiling and longer range than the Lancaster, having a maximum altitude of 35,000 ft. The prototype Lancaster IV was assembled by Avros experimental flight department at Manchesters Ringway Airport, separate production lines were also set up in Canada and Australia, although with the end of the war, production in Canada was halted after only one aircraft had been built. Production in Australia proceeded, the Lincolns that were manufactured there were operated by the Royal Australian Air Force. One Lincoln B Mk XV pattern aircraft was completed in Canada by Victory Aircraft. Along with two aircraft on loan from the RAF, the type was briefly evaluated postwar by the RCAF. The Lancaster V/Lincoln II differed mainly in that it was fitted with Merlin 68A engines, before the Lincoln was developed, the Australian government intended its Department of Aircraft Production, later known as the Government Aircraft Factory, would build the Lancaster Mk III. In its place, a variant of the Lincoln I, re-designated as Mk 30, was manufactured between 1946 and 1949, it has the distinction of being the largest aircraft built in Australia. Orders for a total of 85 Mk 30 Lincolns were placed by the RAAF, the first five Australian examples, were assembled using British-made components. On 17 March 1946, A73-1 conducted its début flight, the first entirely Australian-built Lincoln, the Mk 30 initially featured four Merlin 85 engines, this arrangement was later changed to a combination of two outboard Merlin 66s and two inboard Merlin 85s. A further improved version, designated as Lincoln Mk 30A. During the 1950s, the RAAF heavily modified some of their Mk 30 aircraft to perform anti-submarine warfare missions, the Mk 31 was particularly difficult to land at night, as the bomber used a tailwheel and the long nose obstructed the pilots view of the runway. 18 aircraft were rebuilt to standard in 1952, gaining new serial numbers. Ten were subsequently upgraded to MR. Mk 31 standard, which included an updated radar and these Lincolns served with No.10 Squadron RAAF at RAAF Townsville, however, the discovery of corrosion in the wing spars led to the types premature retirement in 1961

9.
United Kingdom
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The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom or Britain, is a sovereign country in western Europe. Lying off the north-western coast of the European mainland, the United Kingdom includes the island of Great Britain, Northern Ireland is the only part of the United Kingdom that shares a land border with another sovereign state‍—‌the Republic of Ireland. The Irish Sea lies between Great Britain and Ireland, with an area of 242,500 square kilometres, the United Kingdom is the 78th-largest sovereign state in the world and the 11th-largest in Europe. It is also the 21st-most populous country, with an estimated 65.1 million inhabitants, together, this makes it the fourth-most densely populated country in the European Union. The United Kingdom is a monarchy with a parliamentary system of governance. The monarch is Queen Elizabeth II, who has reigned since 6 February 1952, other major urban areas in the United Kingdom include the regions of Birmingham, Leeds, Glasgow, Liverpool and Manchester. The United Kingdom consists of four countries—England, Scotland, Wales, the last three have devolved administrations, each with varying powers, based in their capitals, Edinburgh, Cardiff and Belfast, respectively. The relationships among the countries of the UK have changed over time, Wales was annexed by the Kingdom of England under the Laws in Wales Acts 1535 and 1542. A treaty between England and Scotland resulted in 1707 in a unified Kingdom of Great Britain, which merged in 1801 with the Kingdom of Ireland to form the United Kingdom of Great Britain and Ireland. Five-sixths of Ireland seceded from the UK in 1922, leaving the present formulation of the United Kingdom of Great Britain, there are fourteen British Overseas Territories. These are the remnants of the British Empire which, at its height in the 1920s, British influence can be observed in the language, culture and legal systems of many of its former colonies. The United Kingdom is a country and has the worlds fifth-largest economy by nominal GDP. The UK is considered to have an economy and is categorised as very high in the Human Development Index. It was the worlds first industrialised country and the worlds foremost power during the 19th, the UK remains a great power with considerable economic, cultural, military, scientific and political influence internationally. It is a nuclear weapons state and its military expenditure ranks fourth or fifth in the world. The UK has been a permanent member of the United Nations Security Council since its first session in 1946 and it has been a leading member state of the EU and its predecessor, the European Economic Community, since 1973. However, on 23 June 2016, a referendum on the UKs membership of the EU resulted in a decision to leave. The Acts of Union 1800 united the Kingdom of Great Britain, Scotland, Wales and Northern Ireland have devolved self-government

10.
Handley Page Halifax
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The Handley Page Halifax was British four-engined heavy bomber of the Second World War. On 25 October 1939, the Halifax performed its maiden flight and it quickly became a major component of Bomber Command, performing routine strategic bombing missions against the Axis Powers, many of which were performed at night. The Halifax was also operated in large numbers by other Allied and Commonwealth nations, such as the Royal Canadian Air Force, Royal Australian Air Force, Free French Air Force and Polish forces. Various improved versions of the Halifax were introduced, which incorporated more powerful engines and it remained in service until the end of the war, performing a variety of duties in addition to bombing. Additionally, specialised versions of the Halifax were developed for troop-transport, during the post-war years, the Halifax was operated by the Royal Egyptian Air Force, the French Armée de lAir and the Royal Pakistan Air Force. The type also entered service for a number of years. A dedicated civil variant, the Handley Page Halton, was also developed and entered airline service. During 1961, the last remaining Halifax bombers were retired from operational use, in the 1930s, the Royal Air Force was primarily interested in twin-engine bombers. These designs put limited demands on engine production and maintenance, both of which were stretched with the introduction of so many new types into service. Power limitations were so serious that the British invested heavily in the development of engines in the 2,000 horsepower class in order to improve performance. During the late 1930s, none of these were ready for production, accordingly, in 1936, the RAF also decided to investigate the feasibility of the four-engined bomber. During the mid 1930s, the British Air Ministry formulated and released Specification P. 13/36, in response, Handley Page produced the twin-engine HP56 design to meet Specification P. 13/36. Handley Page aircraft designer George Volkert had responsibility for the design.24 or Bristol Hercules engines, the majority of these engines were under development at this point, while four-engined bomber designs were considered for specification B. In February 1937, following consideration of the designs by the Air Ministry, accordingly, during April 1937, a pair of prototypes of both designs were ordered. The introduction of the successful P. 13/36 candidates was delayed by the necessity of ordering additional Armstrong-Whitworth Whitley, in mid-1937, it was decided to order both the Avro 679 and HP56 designs off the drawing board in order to speed up delivery timetables. The redesign increased the wingspan from 88 ft to 99 ft, towards the end of the year, a full mock-up of the design was assessed, in March 1938, the construction of the pair of HP57 prototypes commenced. Further design modifications resulted in the aircraft, which had been considerably enlarged and was powered by an arrangement of four 1,280 hp Rolls-Royce Merlin X engines. On 17 August 1940, the first flight of the prototype, L7245

11.
Short Stirling
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The Short Stirling was a British four-engined heavy bomber of the Second World War. It has the distinction of being the first four-engined bomber to be introduced into service with the Royal Air Force, the Stirling was designed during the late 1930s by Short Brothers to conform with the requirements laid out in Air Ministry Specification B. 12/36. When the preferred Type 317 had to be abandoned, the S.29, during early 1941, the Stirling entered active squadron service. The Sterling had a brief operational career as a bomber before being relegated to second line duties from late 1943. A handful of ex-military Stirlings were rebuilt and saw continued use on the civil market, in the 1930s, the Royal Air Force was interested primarily in twin-engine bombers. These designs put limited demands on engine production and maintenance, both of which were stretched with the introduction of so many new types into service. Power limitations were so serious that the British invested heavily in the development of engines in the 2,000 horsepower class in order to improve performance. During the late 1930s, none of these were ready for production, accordingly, in 1936, the RAF also decided to investigate the feasibility of the four-engined bomber. Amongst the several requirements specified, the load was to be a maximum of 14,000 lb carried to a range of 2,000 miles or a lesser payload of 8,000 lb to 3,000 miles. It was to have a crew of six and was to have a normal weight of 48, 000lb, while a maximum overload weight of 65. The aircraft would have to be capable of cruising at speeds of 230 mph or greater while flying at 15,000 ft, while possessing three individual gun turrets for self-defence. Additionally, the aircraft should also be able to be used as a troop transport for 24 soldiers. The concept was that the aircraft would fly troops to far corners of the British Empire, to help with this task as well as ease production, it needed to be able to be broken down into parts, for transport by train. Various companies responded to B. 12/36, including Supermarine and Armstrong Whitworth, Shorts were producing several four-engined flying boat designs of the required size and created their S.29 proposal by removing the lower deck and boat hull of the S.25 Sunderland. As originally designed, the S.29 was considered to be capable of favourable high-altitude performance, in October 1936, the S.29 was low down on the short list of designs considered and the Supermarine Type 317 was ordered in prototype form in January 1937. However it was decided that a design to Supermarine was needed for insurance. Shorts accepted this large amount of redesign work, the project had added importance due to the death of Supermarines designer, Reginald Mitchell, which had generated doubt within the Air Ministry. The S.29 used the Sunderlands 114 ft wing and it had to be reduced to less than 100 ft, in order to get the needed lift from a shorter span and excess weight, the redesigned wing was thickened and reshaped

12.
Rolls-Royce Merlin
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The Rolls-Royce Merlin is a British liquid-cooled V-12 piston aero engine of 27-litres capacity. Rolls-Royce designed the engine and first ran it in 1933 as a private venture, initially known as the PV-12, it was later called Merlin following the company convention of naming its piston aero engines after birds of prey. After several modifications, the first production variants of the PV-12 were completed in 1936, the first operational aircraft to enter service using the Merlin were the Fairey Battle, Hawker Hurricane and Supermarine Spitfire. A series of rapidly applied developments, brought about by wartime needs, markedly improved the engines performance, post-war, the Merlin was largely superseded by the Rolls-Royce Griffon for military use, with most Merlin variants being designed and built for airliners and military transport aircraft. Production ceased in 1950 after 160,000 engines had been delivered, Merlin engines remain in Royal Air Force service today with the Battle of Britain Memorial Flight, and power many restored aircraft in private ownership worldwide. The PV-12 was first run on 15 October 1933 and first flew in a Hawker Hart biplane on 21 February 1935, the engine was originally designed to use the evaporative cooling system then in vogue. This proved unreliable and when supplies of ethylene glycol from the U. S. became available, the Hart was subsequently delivered to Rolls-Royce where, as a Merlin testbed, it completed over 100 hours of flying with the Merlin C and E engines. In 1935, the Air Ministry issued a specification, F10/35, fortunately, two designs had been developed, the Supermarine Spitfire and the Hawker Hurricane, the latter designed in response to another specification, F36/34. Both were designed around the PV-12 instead of the Kestrel, and were the only contemporary British fighters to have been so developed, production contracts for both aircraft were placed in 1936, and development of the PV-12 was given top priority as well as government funding. Following the company convention of naming its piston engines after birds of prey, Rolls-Royce named the engine the Merlin after a small. Two more Rolls-Royce engines developed just prior to the war were added to the companys range and this was to be used in larger aircraft such as the Avro Manchester. Although the Peregrine appeared to be a design, it was never allowed to mature since Rolls-Royces priority was refining the Merlin. As a result, the Peregrine saw use in two aircraft, the Westland Whirlwind fighter and one of the Gloster F. 9/37 prototypes. The Vulture was fitted to the Avro Manchester bomber, but proved unreliable in service and the planned fighter using it – the Hawker Tornado – was cancelled as a result. With the Merlin itself soon pushing into the 1,500 hp range, the Griffon incorporated several design improvements and ultimately superseded the Merlin. Early production Merlins were also unreliable, Common problems were cylinder head cracking, coolant leaks, the prototype, developmental, and early production engine types were the, PV-12 The initial design using an evaporative cooling system. Two built, passed bench type testing in July 1934, generating 740 horsepower at 12, Merlin B Two built, ethylene glycol liquid cooling system introduced. Passed Type Testing February 1935, generating 950 horsepower at 11, Merlin C Development of Merlin B, crankcase and cylinder blocks became three separate castings with bolt-on cylinder heads

Bristol Hercules engine. Note the absence of pushrods on the cylinders. Each cylinder has two exhaust ports on the front (short L-shaped tubes) and three intake ports on the back supplied through a single manifold.